I've been pondering the same problem that is gonna come to my garden in the next few months once it starts warming up.. I currently use a modified dehumidifier as a chiller for my flood and drain resivoirs, a 50 gal, a 25 gal and my 55 gallon RO water storage container.. I use the cooling side of the dehumidifier and bend it down into a Rubbermaid container which I will be upgrading to a good sized ice/party cooler because its insulated from the get go.... (I plan to anyhow, I'm hoping it works out as it's tough to bend the cooling fins without breaking the piping if you bend it too much)..
the cooler will hold the water that the dehumidifier/chiller will chill; then as I do already... I'll use submersible pumps to send the chilled water to a coiled up section of 1/2" pex or if $ permits; stainless wort chillers (used for beer making) that runs the water from the chilled water storage container; to one end of the pex coil/wort chiller, through the coil eventually cooling the res or whatever you're trying to cool down and then return the water out of the other end of the coil back to the cooler or whatever type of receptical used fo hold the chilled water basically making each resivoir or whatever I need chilled; an individual closed loop...
picture a home heating boiler as the water receptical and the circulation pumps in the system as the submersibles, but instead of heating baseboard, air handlers or radiant heat.... your chilling a coil that keeps your nute solution cool/at the proper temps in basically the same manner.. basically the chiller keeps the water cold, when whatever res needs cooling; the submersible kicks on and sends chilled water to the coil in the res and back until its satisfied... this will require a themostatic device for each, I've found them for about $25 on amazon, it kicks on at whatever temp you want and shuts down in the same manner... if $ is tight you can use timers to get going but it takes time to get it working right but will work just fine...
I was able to chill 130+ gallons of nute solution/water with this system using a medium sized dehumidifier (I can't remember which size, I think it's a 45 pint) which I paid $130 second hand for I think; yet the thing was brand new basically, along with 3 - 340 gph submersibles and 200' of 1/2" pex tubing which cost about $25 per 100 foot coil I think.. I used for pex for the cooling coils cuz I couldn't afford the wort chillers at that point so i made the pex loops/coils up quick fast and simple to get it running fast and cheap... I think it cost me less than $250-300 total to chill all that water (obviously not including the required electricity)....but that's fairly cheap considering what actual chillers cost nevermind the cost of other items required...
However, in the coming months my chilling system is going to get a whole lot more complicated as I currently keep my mothers in soil but have been switching over to individual dwc buckets each time I clone one of my different strains... I'm doing this because I feel it will simplify things by being able to use the same nutes for everything most importantly, but also as important... getting all of the soil out of my grow rooms... I also like the control I will have of each mother... the idea of being able to up the nutes if I want faster growth to get a mother ready for a major cloning if need be or keep nutrient levels low if I want them to grow slowly is a worthy trade off for the loss of the forgiving nature of soil... ontop of that I can pretty much cut the light level from a 600 on full blast along with a 4' T8 x 6 bulbs to just the 600 dialed down to 400 or so watts on my light mover...
For me, the reason I don't buy or just build a simple multi site ebb and flow system that uses a single large resivoir and control bucket and just chill the 55 gallon res...and do all this extra work of running individual dwc buckets is because I don't want connected system and as I mentioned I won't be able to control each plant aside from the possibility that if one gets sick/root rot they're all getting it most likely... in most cases I won't ever be flowering these mothers so keeping them separate is best for my situation... if your running a system that will run plants veg to flower then a rdwc, multi site ebb and flow or undercurrent system that can be chilled via a single chiller without all the insanity of plumbing a multitude of single buckets like I plan to, than you probably got the right idea...
Also, another FYI....I personally believe in running only water through chillers and using individual pumps and coils as you can see from the above mentioned way I chill everything... but running water only through your chiller to chill whatever you need cooled rather than running nutrient solution through the chiller is the best option as your running the risk of having a nice mess from root rot or the like going through the chiller if shit does go bad... it's a bit more $ and work this way, but you'll only ever be running clean water through your chiller which will also make it last longer imo...
Sorry for the long post, a bad/good habit of mine depending on how you look at it...